(1) Field of the Invention
The present invention relates to ocean wave measurement devices and more specifically to a means for determining realtime ocean wave heights, characteristics, and statistics such as mean wave heights, power spectral densities, and sea state from locations below the sea surface such as on a submerged platform or on the sea bottom.
(2) Description of the Prior Art
Users of ocean wave information are many and varied. Naval architects, ocean engineers and oceanographers frequently measure wave statistics in order to properly design and construct ships, platforms and structures. Meteorologists measure waves as an aid in predicting and studying weather patterns. The U.S. Navy has great interest in measuring surface wave conditions from submerged submarines due to the profound effect that the surface waves have, not only on the decision to launch submarine missiles, but also upon the potential destabilization of the launching submarine itself.
Various methods are currently available for measuring ocean surface wave heights, statistics, and sea surface characteristics from below the ocean surface. Such sensing methods include pressure sensors, acoustic sensors, and tethered accelerometer instrumented buoys. Each sensor is capable of providing wave height data for determining statistics and surface characteristics but each sensor has inherent practical limitations such that its use may be inappropriate for given applications. For example, pressure sensors cannot generally be used at depths greater than 20 meters below the sea surface. Acoustic sensors are not used very often because naturally occurring variations in ocean temperature and salinity affect the speed of sound in sea water and hence the calibrated accuracy of the acoustic sensor. Tethered buoys launched from U.S. Navy submarines, such as the one described in U.S. Pat. No. 4,794,575, can be used to measure surface wave conditions but tend to increase the risk of submarine counterdetection by hostile forces. In addition, tethered buoys can limit submarine operating capabilities by placing restrictions on permissible submarine speed and depth for the period during which the buoy is deployed.
During recent U.S. Navy submarine underwater missile launching exercises, failures have occurred that have been directly attributed to the destabilization of the missile and the launching platform by large ocean surface waves, i. e., high sea state. Due to the adverse effects of these large surface waves on the missile and the launch platform, a principal criteria for arriving at a launch decision is the maximum sea-state launch design limit of the missile in relation to the actual sea-state conditions present at the time of launch. Currently the submarine commander is required to make critical sea-state estimates using one or both of two methods presently available to him. These methods comprise either periscope observations of short duration or second party observation reports received via communication link. Both of the methods have drawbacks but the most significant problem is that for each case the submarine is required to approach the surface to periscope depth. This greatly increases the risk of counterdetection by hostile forces. There is currently no objective, reliable, and covert method by which a submarine can determine the required real-time sea-state conditions prior to launch of sea-state limited missiles. What is needed is a covert sensor.